Shell Dry Weight Research Articles

Influences of temperature, salinity and available food upon suspended culture of the Pacific oyster, Crassostrea gigas: II. Condition index and survival

Condition indices, dry meat weight:dry shell weight ratio and dry meat weight:internal volume ratio, and survival rate were determined for a common broodstock of oysters grown in 10 locations in British Columbia, Canada, over a 14-month period. Year 0 oysters (20–30 mm initial shell height) had lower overall survival rates (31.5–57.3%) than Year 1 oysters (40–50 mm shell height) (63.2–89.7%) although for a given age-class, differences in survival between most sites were not great. Most oyster mortalities occurred in the initial 2–3 months according to seasonal and annual instantaneous mortality rates. Monthly dry meat weight:internal volume condition index values did not appear to be related to site-related trends in growth rate. Dry meat weight:dry shell weight ratio was a more suitable index for assessing the condition of oysters provided available food and water temperature were the principal factors affecting growth. Slow growing oysters from areas with low salinity (< 20 ppt) had dry meat weight:shell weight ratios equivalent to those of rapidly growing oysters from areas with conditions of high salinity and abundant food supply. Intra-site correlations between the two condition indices were poor. Multiple regression analysis revealed that dry meat weight:internal volume ratio was primarily correlated to whole weight and secondarily to water temperature, salinity and chlorophyll a concentration ( r 2 = 0.39, P ≤ 0.001). Dry meat weight:dry shell weight ratio was correlated to the same environmental factors but not whole weight ( r 2 = 0.41, P ≤ 0.001). Ecophysiological studies of oysters should not rely extensively upon results of condition index analysis, particularly involving volume measurements, unless there are collaborating growth and environmental data.

Winter growth of the blue mussel Mytilus edulis L.: importance of stock and site

To investigate the influence of genetics and environment on the growth of Mytilus edulis at low temperatures, we transplanted juveniles from 11 stocks to 10 sites along the coast of Nova Scotia, Canada. For each stock at each site, the mean change in shell length, dry shell weight, dry tissue weight and viability from early November 1985 to mid-April 1986 were documented. Stock and site differences were important in explaining the variance in shell growth (length and weight) but site alone accounted for most of the variation in tissue growth. Tissue growth was higher at ice-free sites than at ice-covered sites, but shell growth was similar among sites. We speculate that tissue growth was food-limited at those sites where ice-coverage delayed the onset of the spring phytoplankton bloom.

Biometric studies on the bivalvesAstarte elliptica, A. borealis andA. montagui in Kiel Bay (Western Baltic Sea)

The threeAstarte species were studied in June 1983 at two sites in Kiel Bay, “Suderfahrt” and “Schleimunde”, at 20 m depth. Shell length to live wet weight correlations are given for all three species; forA. elliptica also shell-free dry weight, shell dry weight, ash-free dry weight of the soft body and ash-free dry weight of the shell are recorded as functions of the shell length. In the logarithmic length/weight regression analysis the coefficients of slope forA. elliptica andA. borealis are 3. ForA. montagui, that coefficient is significantly greater than 3. Weight conversion factors, calculated forA. elliptica, revealed a mean weight composition of 31.5 % water in the mantle cavity and tissue water, 64.5 % shell ash, 2.1 % organic content of shell, 1.7 % organic content of the soft body and 0.4 % ash of the soft body. An isometric growth of shell length and shell breadth is confirmed forA. borealis, whileA. montagui exhibits positive allometric shell growth and changes its shape during life.

The use of physiological condition indices in marine bivalve aquaculture

The physiological condition indices most commonly used in bivalve aquaculture are reviewed and evaluated. Two general categories of indices may be distinguished: static and dynamic. Of the static indices reviewed, only one is recommended for use in the culture of early developmental stages — the dry ash weight: total dry weight ratio. In the case of juveniles and adults, the easily-measured dry tissue weight: dry shell weight is recommended for most routine work. The dynamic indices reviewed are based on production estimates, and hence reflect physiological changes over specified time intervals. Of these indices, only net growth efficiency is recommended for use in bivalve aquaculture, and it is applicable to all life stages. While this index gives the most information about the physiological state of the animals comprising a population, it is very difficult to evaluate and is thus most appropriate as a research tool.

Estimating the biomass of freshwater mussels (Bivalvia: Unionidae) from shell dimensions

We have compared the convenience and accuracy of two models using 6 shell dimensions for predicting 4 biomass parameters for 4 species of southern U.S.A. unionids (Quadrula quadrula, Q. pustulosa, Lampsilis anodontoides, and Amblema perplicata). Prediction of whole wet weight, tissue wet weight, tissue dry weight, and shell dry weight as a linear function of (shell length)3 was accurate, even with extremely small sample sizes. In addition, this method is very convenient for field use because it requires one simple, unambiguous shell measurement.

The Influence of Layer Flock Age on Egg Component Yields and Solids Content

Two experiments were conducted to determine the influence of layer flock age on egg component yields and solids content of the yolk and albumen. Experiment 1 was conducted on eggs collected during February from six commercial farms with the same strain (Shaver) of birds ranging in age from 26 to 58 weeks and fed the same dietary energy and protein levels. The total and relative amounts of shell, yolk, and albumen were determined using two separation techniques and the total solids were determined for the yolk and albumen. Experiment 2 was conducted in August using four commercial flocks of Shaver hens ranging in age from 29 to 6 2 weeks. The eggs were analyzed as in Experiment 1 using the separation technique that resulted in the lowest coefficient of variation.Results indicated that as layer flock age increases, egg weight, dry shell weight, deformation and percent yolk increased, percent shell, percent albumen and percent albumen solids decreased, and percent yolk solids exhibited no consistent patterns. These differences would result in an approximately 2% increase in dry yolk solids by using eggs from older hens.

Aerial exposure and energy input in the bivalve Choromytilus meridionalis (Kr.)

The effects of aerial exposure on growth, filtration, and assimilation were examined in Choromytilus meridionalis (Kr.) from Bailey's Cottage, False Bay, South Africa. The maximum height at which these mussels occur on the shore corresponds to 50% aerial exposure. Growth rates declined with increasing shore height. The relationships between flesh and shell dry weight and shell length were not significantly different in littoral and sublittoral mussels. Littoral mussels did not show enhanced filtration rates or assimilation efficiencies relative to continually submerged individuals. Thus, littoral mussels experience a decline in ingestion ration which is directly correlated with increasing shore height. Under conditions of limited food availability littoral organisms frequently employ conservative mechanisms to limit energy expenditure. In C. meridionalis this is evidenced by limitation of the growth rate. Energy conservation may also be facilitated by quiescence and reduced respiratory cost during exposure. This requires investigation.

Physical characteristics of intact and cracked eggs

1. Six egg samples, comprising equal numbers of intact and cracked eggs, were collected from three flocks of hybrid layers. 2. Cracks were classified according to type (hole, star or straight) and the weight, shape, shell colour and specific gravity of all the eggs were measured. Shell thickness and dry shell weight were also recorded for a maximum of 10 intact and 10 cracked eggs from each sample. 3. The largest proportion of cracks were holes. 4. Differences in mean egg weight and shape of intact and cracked eggs within each sample were inconsistent. Mean shell colour was darker for the intact brown eggs than for the cracked ones. For all the samples, mean egg specific gravity, shell thickness and dry shell weight were higher for the intact eggs. The difference in egg specific gravity was significant (P<0.05) for all samples. 5. Holes occurred in eggs of lower mean weight but with better quality shells than those in which star or straight cracks occurred.

The effect of temperature on growth, physiology, and gametogenesis in the Manila clam Tapes philippinarum (Adams & Reeve, 1850)

Populations of the Manila clam, Tapes philippinarum (Adams & Reeve, 1850), were maintained at temperatures of 12, 15, 18, and 21°C for a period of 19 weeks. Regular determinations were made of ammonia excretion rate following which animals were sacrificed for estimation of dry meat weight, dry shell weight, biochemical composition, and gonadal development. T. philippinarum increased from an initial dry meat weight of 291.5 mg to final values of 957.9, 733.0, 735.0, and 586.0 mg at 12, 15, 18, and 21 °C, respectively. An initial increase in percentage carbohydrate content was evident at all temperatures. This was followed by carbohydrate depletion associated with gametogenesis, the transition from accumulation to depletion occurring earlier with increasing temperature. Ripe gonadal material was evident at all temperatures, but spawning was only evident at 15, 18, and 21 °C. Ammonia excretion at 12, 15, and 18°C showed an allometric relationship to meat weight; this was not so at 21 °C.

Some biochemical and physiological aspects of growth and gametogenesis inCrassostrea gigasandOstrea edulisgrown at sustained elevated temperatures

Crassostrea gigas (Thunberg) andOstrea edulis L.were grown at sustained temperatures of 12°, 15°, 18° and 21°C for a period of 19 weeks. Regular assays of weight specific ammonia excretion rate were made, following which animals were sacrificed for estimation of dry meat weight, dry shell weight, biochemical composition (percentage carbon, nitrogen, carbohydrate, ash) and gonadal development (histological assessment). Crassostrea gigas grew from an intial live weight of 5·2 g to values of 23·5, 28·2, 34·6 and 38·7 g at 120, 150, 180 and 21 °C respectively.

The effect of intertidal exposure on the growth and survival of hatchery-reared Pacific oysters ( Crassostrea gigas Thunberg) kept in trays during their first ongrowing season

In a number of trials during 1971 and 1972 small populations of hatchery-reared Pacific oyster spat ( Crassostrea gigas Thunberg) 0.07–4.1 g mean live weight, were grown intertidally in trays to measure the effect of exposure to air on growth and survival. In the Menai Straits, N. Wales, and at Paglesham Pool, R. Roach, Essex, several stations were selected above low water of spring tides (LWST) to cover the range of 0–30% exposure to air. Live weight, dry meat weight and dry shell weight were reduced with increased exposure to air, but the ratio of dry meat weight to dry shell weight (shell condition index), the gross biochemical composition, and survival were not affected. By extrapolation the point of no growth was found to be at 36 and 47% exposure to air at the sites in the Menai Straits and R. Roach, respectively.

GROWTH RATE, LONGEVITY AND MAXIMUM SIZE OFMACOMA BALTHICA(L.)

1. Growth rate and longevity were determined for a population of M. balthica at Rand Harbor, Falmouth, Mass., using a modification of the mark and recapture technique that allowed all marked individuals to be followed throughout a year. Dry weight biomass, dry shell weight and caloric content were also determined. 2. Caloric content is 4.049 kcal/ash-free g. Dry weight biomass and dry shell weight were found to have a similar allometric growth with a constant of allometry of approximately 3 when measured against shell length. 3. The bivalves were discovered to grow year round with the peak period of growth occurring from May to August. A negatively linear relationship between initial length (X) and total annual increment (Y) was found (Y= -0.59 X + 12.85). 4. The growth curve for the Rand Harbor population revealed that within the first two years of life, M. balthica attains most of its total length. Growth ceases once a maximum size of 22-25 mm is reached and total longevity is estimated to be 6-10 years. 5. These results were compared to other studies and the theory that maximum size, growth rate and longevity are controlled by temperature presented and discussed.

Dieldrin and p,p'-DDT effects on egg production and eggshell thickness of chickens.

Sixty Leghorn hens were randomly divided into 5 groups of 12 and individually fed a control diet, or diets containing 10 and 20 ppm dieldrin, or diets containing 100 and 200 ppm p,p′-DDT for a 12-week period. Average egg production per bird, egg weight, dry shell weight, shell thickness (not including membranes), and shell calcium were not affected by feeding the insecticides. In addition, the length of the clutch or the number of clutches during the 12-week period were not affected. However, egg weight increased with time during the experiment, and eggshell thickness decreased with successive eggs within a clutch.